The biosynthesis of epidermal growth factor (EGF) in the adult male mouse submaxillary gland will be studied by characterizing the proteins labeled with (35S) cystine which are specifically precipitated with anti-EGF antiserum. The precursor-product relationship of the labeled species which is larger than EGF to EGF itself will be examined in kinetic and pulse chase labeling experiments, by peptide analysis and by the ability of the trypsin-like subunit which is purified along with EGF to convert this larger species to EGF. The ability of other similar trypsin-like proteins from the gland, such as the gamma-subunits associated with nerve growth factor and the endopeptidase which cleaves one peptide bond in the nerve growth factor chains, to carry out this precursor conversion will be compared. The stability of the complex in which EGF is isolated will be measured in terms of the dissociation of the trypsin-like subunit. The effect of zinc ion on the stability of the complex will be examined and the zinc ion content of the complex determined. Attempts will be made to form hybrid complexes of EGF and the other trypsin-like proteins. The ability of EGF to bind to its specific receptors as it is stabilized in the complex will be examined.